1. Field of the Invention
The present invention relates to a method for optically recording information to an optical information recording medium and particularly to a method for optically recording information at a linear velocity of at least 14 m/s.
2. Description of the Related Art
One conventionally known optical information recording medium is an optical disk on which information can be recorded with a laser beam only one time. Such an optical disk is also called a write-once CD (so called CD-R), whose typical structure includes a recording layer of organic dye, a light reflecting layer of metal such as gold, and a protective resin layer stacked in this order formed on a transparent substrate disk. When information is recorded, a near-infrared laser beam (generally with a wavelength of about 780 nm) is applied to such CD-Rs, an irradiated portion of the recording layer absorbs the beam and thus is locally heated and optical characteristics of the irradiated portion change physically or chemically (for example, pits are formed). When the information is read (played back), a laser beam having the same wavelength as that used for recording irradiates the optical disk to detect a difference in reflectivity between a position of the recording layer with the changed optical characteristics (recorded portion) and a position of the recording layer with unchanged optical characteristics (unrecorded portion).
In recent years, there has been a demand for a higher density optical information recording medium. In response to such a demand, a proposal is an optical disk called “write-once Digital Versatile Disk” (so called DVD-R). The structure of such DVD-Rs includes: a transparent substrate disk having a guide groove (pre-groove) (0.74 to 0.8 μm) to be tracked by an irradiated laser beam (such a pre-groove is at least twice as more narrow as that of CD-R); a recording layer that includes a dye and is formed on the substrate; a light reflecting layer generally formed on the recording layer; and optionally a protective layer, wherein two disks each having the aforementioned layers or the disk having the aforementioned layers and a protective substrate disk with the same shape are bonded with an adhesive in such a manner that the recording layer is placed inside. Recording and playback are performed by irradiating a visible laser beam (generally with a wavelength in the range of from 630 nm to 680 nm) to the DVD-R. The recording density of DVD-R can be made higher than that of CD-R.
With respect to such DVD-Rs, recently, there has been a growing demand for a high recording speed of 4× or more (a linear velocity of at least 14 m/s). It is known that optimal recording power for an optical information recording medium is approximately proportional to the square root of recording speed. For example, the optimal recording power at a recording speed of 4× is about twice as high as that at 1×. As the recording speed increases, the energy applied for a short time increases, and thus the deformation of the recorded pit portion tends to increase. A greater deformation of the recorded pit can produce a higher degree of modulation so that the playback signal C/N can be higher. In such cases, however, the signal leak to adjacent tracks increases, in other words, the crosstalk increases. A higher recording density means a shorter track pit and thus crosstalk has a large effect.
When pre-pits having address signals are formed on the land area between the recording tracks like in DVD-Rs, if relatively large pits are formed on the recording track, the address information can become hard to read causing LPP errors to occur.
For example, Japanese Patent Application Laid-Open (JP-A) No. 10-188341 discloses an optical information recording medium in which a recording layer containing an organic dye as a main component has an exothermic peak of from −10 μV/mg to 10 μV/mg for the purpose of solving the problem of crosstalk. In such an optical information recording medium, however, in high speed recording, for example, at a linear velocity of at least 14 m/s, formed pits are too large, which can have an adverse effect on the readout from adjacent tracks or the readout of the address information from the land portion.